Britain's Chief of the Defence Staff General David Richards speaks on the BBC's Andrew Marr Show, in London Nov 14, 2010. The West is fighting a war against al Qaeda in which its forces can contain Islamic militancy but cannot achieve a conventional military victory, Britain's most senior officer was quoted as saying on Sunday. [Photo/Agencies]

KABUL - Five soldiers serving with the NATO-led force in Afghanistan were killed on Sunday, including three in a clash with insurgents in the east, the coalition said, one of the worst daily tolls in a month.

The International Security Assistance Force (ISAF) gave no other details about the incident in Afghanistan's east, including the nationality of those killed. The majority of troops serving in the volatile east are American.

Earlier, ISAF said two of its soldiers had been killed in separate explosions in the south.

The five casualties were the worst suffered by ISAF since Oct 14, when eight people were killed in five separate incidents. Another six were killed the previous day.

Violence across Afghanistan is at its worst since the Taliban were overthrown by US-backed Afghan forces nine years ago, with civilian and military casualties at record levels despite the presence of about 150,000 foreign troops.

At least 642 ISAF troops, about 440 of them American, have been killed in Afghanistan so far in 2010, by far the deadliest year of the war. Another three were killed on Saturday, the ninth anniversary of the fall of the Taliban in Kabul.

The latest casualties will come as a sobering reminder when NATO leaders gather later this week in Lisbon, where Afghanistan will be the top of the agenda.

Many European NATO leaders are feeling increasing pressure to justify their continued support for the drawn-out war.

The deaths also come before US President Barack Obama is set to review his Afghanistan war strategy in December amid sagging public support.